Methods and apparatus for rapidly measuring pressure in earth formations

ABSTRACT

Methods and apparatus for rapidly measuring pressure in earth formations are disclosed. According to a first embodiment of the apparatus, a probe is provided with a movable piston having a sensor built into the piston. According to a second embodiment of the apparatus, the pressure sensor is mounted adjacent to or within the piston cylinder and a fluid pathway is provided from the sensor to the interior of the cylinder. Methods of operating the first and second embodiments include delivering the probe to a desired location in a borehole, setting the probe against the formation, and withdrawing the piston to draw down fluid for pressure sensing. A third embodiment of the probe is similar to the second but is provided with a spring loaded metal protector surrounding the cylinder and an annular rubber facing. The third embodiment is preferably used in a semi-continuous pressure measuring tool or an LWD tool having a piston controlled bowspring and a piston controlled articulated member carrying the probe. The tool is moved in a semi-set mode and when located at a desired depth is rapidly put in a fully-set mode.

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 10/285,788, filed Nov. 1, 2002, assigned to thesame assignee as the present application, and incorporated herein byreference.

[0002] This application is related to co-owned U.S. Pat. Nos. 4,936,139and 4,860,581, the complete disclosures of which are hereby incorporatedby reference herein.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The invention relates to the production of hydrocarbons from anunderground formation. More particularly, the invention relates totesting earth formations to determine formation pressure.

[0005] 2. State of the Art

[0006] The previously incorporated co-owned U.S. Patents describetechnology used in the assignee's commercially successful borehole tool,the MDT (a trademark of Schlumberger). The MDT tool is a wireline toolwhich includes a packer and a probe which enable the sampling offormation fluids and the measuring of pressure transients duringsampling or a pretest. One can infer formation permeability from apressure transient. In addition, the formation pressure can be obtainedwith the MDT tool by extrapolation from the pressure transient or,preferably, by waiting long enough for the measured pressure transientto stabilize.

[0007] Prior art FIG. 1 illustrates an MDT tool as described inpreviously incorporated U.S. Pat. Nos. 4,936,139 and 4,860,581. The MDTtool 10 is shown in a borehole 12. The tool 10 includes an elongatedbody 14 that carries a selectively extendible fluid admitting assembly16 and a selectively extendible tool anchoring member 18. Theillustrated tool also has at least one fluid collecting chamber 20 whichis coupled to the fluid admitting assembly 16 by a flow line bus 22. Thefluid admitting assembly 16 includes a packer 24, a pair of pistons 26and a front shoe 28 connecting the packer to the pistons. A filter 30extends through the packer and the front shoe to a filter valve 32. Thevalve 32 is selectively fluidly coupled to the collecting chamber 20 bythe flow line bus 22 which is also connected to a strain gauge 34, acrystal quartz gauge (CQG) 36, a resistivity/temperature cell 38, and apretest chamber 40 via an isolation valve 42 and an equalizing valve 44.

[0008] In order to make accurate analyses of the formation, it isdesirable to obtain many pressure measurements throughout differentparts of the formation. In addition, because of the expense involved inkeeping the MDT tool deployed in a borehole, it is desirable thatmeasurements and samples be taken as quickly as possible. For highpermeability formations, the MDT tool provides formation pressuremeasurements reasonably quickly, two to three minutes per point, much ofthis time being taken to anchor the tool. For low permeabilityformations, however, it may take several more minutes for the pressureto stabilize. It will be appreciated that the steps involved in takingpressure measurements include raising or lowering the tool to a desiredlocation, extending the telescoping pistons and the packer to anchor thetool, extending the fluid collecting filter up to the wall of theformation, pumping to remove mud cake and ensure hydraulic communicationwith the formation, waiting for the pressure to stabilize, thenretracting the packer and pistons before moving to the next measurementlocation.

SUMMARY OF THE INVENTION

[0009] It is therefore an object of the invention to provide methods andapparatus for rapidly measuring pressure in earth formations.

[0010] It is also an object of the invention to provide methods andapparatus for rapidly measuring pressure in earth formations having lowpermeability.

[0011] In accord with these objects that will be discussed in detailbelow, the apparatus of the present invention includes a piston drivenprobe having an integral or closely associated pressure sensor. It hasbeen discovered that one of the reasons why the existing MDT tool andtools like it are slow to measure pressure is because they havevoluminous flow lines with dead ends that are liable to trap otherfluids. This is generally desirable in the MDT tool for the acquisitionof fluid samples, but it makes pressure measurements time consuming dueto the wait for the flow lines to adjust to the pressure.

[0012] According to a first embodiment of the invention, anhydraulically operated probe assembly is provided with an integral MEMS(microelectro mechanical system) or similar miniature pressure andtemperature sensor. The probe assembly is designed to be used with thehydraulic system of an existing MDT tool. The probe assembly includes anhydraulically operated piston with the sensor embedded therein. A fluidpathway of sufficient tortuosity (e.g. a zig-zag path capable of holdingviscous hydraulic fluid as a protector of the sensing diaphragm) isprovided from the head of the piston to the sensor and is filled with aviscous hydraulic fluid. Alternatively, a less tortuous path is providedwith a diaphragm which separates the hydraulic fluid from the formationfluids. The piston is preferably provided with an O-ring seal between itand the probe body.

[0013] According to a second embodiment of the invention, the sensor isnot mounted in the piston but is mounted in the body of the probe and iscoupled to a fluid pathway which terminates in an interior side wall ofthe piston cylinder. The piston is provided with an O-ring at a locationwhich does not pass over the side wall terminus of the fluid pathway.

[0014] According to a third embodiment of the invention, asemi-continuous formation pressure tool is provided. An exemplary toolhas a bow spring and a telescoping piston. The bow spring exerts a lightforce against the formation wall whose traveling force can be adjustedby the piston. For fully setting the tool, an inner piston capable ofmoving through a hole in the bow spring may be used. This allows thetool to travel in the nearly set mode with negligible time required tobe placed in the fully set mode. This embodiment can also be adapted foruse in a logging while drilling (LWD) tool.

[0015] Additional objects and advantages of the invention will becomeapparent to those skilled in the art upon reference to the detaileddescription taken in conjunction with the provided figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a schematic view of a prior art MDT tool;

[0017]FIG. 2 is a schematic view of a first embodiment of a pressuresensing probe according to the invention;

[0018]FIG. 2a is a schematic view of an alternate first embodiment of apressure sensing probe according to the invention;

[0019]FIG. 3 is a schematic view of a second embodiment of a pressuresensing probe according to the invention;

[0020]FIG. 4 is a schematic view of a third embodiment of a pressuresensing probe according to the invention;

[0021]FIG. 5 is a schematic view of a semi-continuous formation pressuretool according to the invention; and

[0022]FIG. 5a illustrates more detail of an embodiment of the piston andbow spring of FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Referring now to FIG. 2, the probe 100 includes an hydrauliccylinder 102 having a first fluid inlet 104 and a second fluid inlet 106with a first piston 108 disposed therebetween. The fluid on either sideof the piston 108 is sealed by an O-ring 110. A second piston 112, whichis attached to or integral with the first piston 108, extends from thefirst piston 108 into a fluid cylinder 114 (attached to or integral withthe hydraulic cylinder 102) and is sealed with an O-ring 116. The secondpiston 112 has a bore 118 which extends into a chamber within the pistoncontaining a pressure sensor 120, covered with a fluid 122 and adiaphragm 124. An electrical cable connection 126 extends from thepressure sensor 120 through the pistons 112, 108 and out through thecylinder 102. The fluid cylinder 114 has a tapered end 128 for insertioninto the formation. A packer 130 (illustrated schematically) ispreferably mounted adjacent the cylinder 114 for moving the cylinderinto and out of the formation. The packer is pushed via a metallic plate132.

[0024] From the foregoing, those skilled in the art will appreciate thatthe introduction of hydraulic fluid into the inlet 106 will cause thepistons 108, 112 to be driven forward. Similarly, introduction ofhydraulic fluid into the inlet 104 will cause the pistons to be drivenback to the position shown in FIG. 2.

[0025] The probe 100 is designed to be used with an existing MDThydraulic system which is utilized to set the packer(s), drive the probeinto or against the formation, and move the pistons 108, 112. The sensor120 is preferably a MEMS (microelectro mechanical system) and the fluid122 is preferably silicone or Fomblin oil. FIG. 2a illustrates analternate first embodiment 100′ wherein a tortuous path 118′ is providedin fluid communication with the sensor 120. The path 118′ is preferablyfilled with a viscous oil.

[0026] According to the methods of the invention, the pistons 108, 112are moved to the forward position (not shown) and the MDT tool islowered or raised to the desired position. The MDT hydraulic system isoperated to energize the setting pistons so that the MDT tool is rigidlyheld at a depth and the packer is set. The setting action is followed bya probe setting wherein the probe 100 is driven toward the formation sothat the formation is engaged by the cylinder 114. This is followed bythe withdrawal of the pistons 108, 112, stabilization of a pressurereading, and then retraction of the probe and the packer(s). The timerequired to make measurements may be reduced by having an automatedalgorithm that computes pressure as a function of spherical/cylindricaltime functions. If the sequence converges to the same value one maydecide to retract, in advance of reaching close to the formationpressure. In other words while extrapolating a final pressure from aseries of measurements, one may decide that the extrapolated value iscorrect when additional measurements do not change the extrapolatedvalue.

[0027] According to the methods described above, it is possible forsoftware to extrapolate formation pressure based on spherical orcylindrical flow (knowing the retraction rate of the piston, or in theabsence of which, specifying a rate pulse of known magnitude). The usermay be allowed to override this option.

[0028] Equation (1) illustrates the spherical flow function f_(s) as afunction of flow time T_(f) and time since flow was stopped Δt.$\begin{matrix}{f_{s} = ( {\frac{1}{\sqrt{\Delta \quad t}} - \frac{1}{\sqrt{T_{f} + {\Delta \quad t}}}} )} & (1)\end{matrix}$

[0029] Equation (2) illustrates the cylindrical flow function f_(c) as afunction of flow time T_(f) and time since flow was stopped Δt.$\begin{matrix}{f_{c} = {\ln \quad ( \frac{T_{f} + {\Delta \quad t}}{\Delta \quad t} )}} & (2)\end{matrix}$

[0030] In order to provide a good clean-up of the mudcake which willaccumulate in the cylinder 114, an ultrasonic horn or an ultrasonicmudcake cleaner (not shown) may be included in the piston 112. Byemploying an ultrasound cleaner the adhesion of the mudcake to theformation can be reduced. In a preferred method, the ultrasonic devicewould be activated as the piston is withdrawn to ease the removal of themudcake.

[0031] Although the presently preferred embodiment is to utilize thehydraulics of a modified MDT tool to operate the probe 100, it will beappreciated that an alternative to the hydraulic system is to activatethe piston in one quick motion with an electromagnetic actuator. Anadvantage of the non-hydraulic system is that the flow rate isessentially a pulse of an extremely short duration. This allows for areduction of the flowing period by several seconds. The force that maybe exerted in such a system is about 100N. Given that the pressuredifferentials between the borehole and the formation fluid may lead toforces as high as 750N for the hydraulic probe, the non-hydraulic probeshould have a diameter approximately one-fourth that of the hydraulicprobe. In particular, the hydraulic probe should have a diameter of 1-2cm and the non-hydraulic probe should have a diameter of 0.25-0.5 cm.

[0032]FIG. 3 shows an alternate embodiment of a probe 200 which issimilar to the probe 100 with similar reference numerals (increased by100) referring to similar parts. In this embodiment, a larger sensor 220(e.g. quartz guage or strain gauge such as a sapphire strain gauge)rather than a smaller MEMS sensor (120 in FIG. 2) is mounted adjacent tothe cylinder 202. A fluid pathway 218 extends from the sensor 220 intothe cylinder 214. The location of the outlet of the pathway 218 isselected such that it is not crossed by the O-ring 216 of the piston212. This embodiment allows the use of sensors which are too large to bebuilt into the body of a piston. The operation of the probe 200 issubstantially the same as the operation of the probe 100 describedabove.

[0033] It may be advantageous for the fluid pathway 218 to be providedwith slits (e.g. a screen, not shown) to prevent the entry of mudparticles. The mud caught by the screen is then dislodged as the piston212 moves forward. According to an alternative embodiment, the pressuresensor 220 can be mounted inside the body of the cylinder 202, thusshortening the length of the fluid path 218.

[0034]FIGS. 4 and 5 illustrate a probe 300 and a tool 400, respectively,for semi-continuous formation pressure testing. The probe 300 is similarto the probe 200 with similar reference numerals (increased by 100)referring to similar parts. According to this embodiment, the cylinder314 has a diameter substantially equal to the cylinder 302 and isprovided by a cylindrical metal protector 350 biased by one or moresprings 352, 354. The annulus inside the metal protector 350 is coveredwith a rubber facing 358. The spring constant of the spring(s) 352 (354)is such that the metal protector 350 protects the rubber facing 358 whenthe probe 300 travels through the borehole. Once a desired depth isreached, the probe 300 is moved toward the formation against the actionof the spring(s) 352 (354) until the rubber facing 358 of the cylinder314 is pressed sufficiently against the formation. The pistons 308, 312are then operated as described above.

[0035]FIG. 5 illustrates a tool 400 which incorporates a probe 300 asdescribed above. The tool 400 includes a bowspring 402 coupled to afirst piston assembly 404 and an articulated assembly 406 coupled to asecond piston 408. The probe 300 is coupled to the end of thearticulated assembly 406. The assembly 406 and the bowspring 402 arepreferably mounted approximately 180 degrees apart.

[0036] As illustrated in FIG. 5a, the piston assembly 404 includes apiston 404 a surrounded by springs 404 b and a piston cylinder 404 c,404 d. Filling cylinder 404 c and draining 404 d retracts the piston.Filling 404 d while draining 404 c extends the piston.

[0037] According to the method of operating the tool 400, the pistons404 and 406 are adjusted such that the bowspring 402 and the metalprotector of the probe 300 exert light pressure against the formation130 when the tool is being lowered into (raised out of) the borehole.The amount of pressure exerted should be sufficiently low to preventdamage to the bowspring and the probe. Once a desired location isreached for a pressure measurement, the pressure exerted by the pistons404, 408 is increased and the tool is rapidly set. To do this, thepiston arrangement may be allowed to travel through a hole in the bowspring as shown in FIG. 5a to directly exert a large force on theborehole wall. Once the tool is set, the pistons 308, 312 are operatedin the manner described above.

[0038] The tool 400 has the advantage that rapid travel is accomplishedin an “almost set mode” and thus the setting time is reduced. Emptyingthe probe 300 by moving the piston forward may be accomplished while thetool 400 is in travel. By lowering the hydraulic setting force duringtravel, a clear pathway for the fluid to be ejected from the probe tothe borehole may be created. To facilitate this even further, the metalprotector 350 around the rubber facing 358 may be provided with radialholes 351 to provide a fluid pathway during fluid ejection.

[0039] The “semi-continuous” tool 400 is also adaptable to thelogging-while-drilling (LWD) environment. When used in an LWDapplication, it may be advisable to provide the tool with additionalsafety features. For example, it may be preferable that the drill stringonly be rotated when the probe and the bowspring are fully-retracted. Inanticipation of a measurement, the tool may run on an almost-set modeand then at the time of measurement on a fully-set mode.

[0040] The concepts of the tool 400 may be extended to include multiplearms with probes to provide several pressure measurements along the toollength. In this case, automatic normalization and calibration of thepressure sensors with respect to each other, by using all of theborehole pressure data while the probes are in a borehole reading mode(fully retracted if necessary) is recommended.

[0041] There have been described and illustrated herein severalembodiments of methods and apparatus for rapidly measuring pressure inearth formations. While particular embodiments of the invention havebeen described, it is not intended that the invention be limitedthereto, as it is intended that the invention be as broad in scope asthe art will allow and that the specification be read likewise. It willtherefore be appreciated by those skilled in the art that yet othermodifications could be made to the provided invention without deviatingfrom its spirit and scope as so claimed.

1. A probe for use with a borehole tool for measuring pressure in anearth formation, said probe comprising: a) a first piston cylinderhaving an end which is movable into contact with the formation; b) afirst piston movable within said first piston cylinder; and c) apressure sensor in fluid communication with said first piston cylinder,wherein said pressure sensor is mounted at one of an interior of saidfirst piston with said fluid communication being provided by a bore inthe first piston, and proximate said first piston with said fluidcommunication being provided by a bore extending through the wall ofsaid first piston cylinder.
 2. A probe according to claim 1, wherein:said pressure sensor is mounted inside said first piston.
 3. A probeaccording to claim 2, wherein: said sensor is a MEMS sensor.
 4. A probeaccording to claim 3, further comprising: d) an electrical conductorwhich extends through said first piston and is coupled to said MEMSsensor.
 5. A probe according to claim 2, further comprising: d) a secondpiston coupled to said first piston; e) a second piston cylinder withinwhich said second piston is movably mounted, wherein movement of saidsecond piston within said second piston cylinder causes movement of saidfirst piston within said first piston cylinder.
 6. A probe according toclaim 5, wherein said second piston defines first and second fluidchambers in said second piston cylinder, each of said fluid chambersbeing provided with a fluid valve such that fluid entering said firstfluid chamber and exiting said second fluid chamber causes said secondpiston to move in a first direction, and fluid entering said secondfluid chamber and exiting said first fluid chamber causes said secondpiston to move in a second direction.
 7. A probe according to claim 2,further comprising: an O-ring surrounding said first piston sealing thespace between said first piston and said first piston cylinder.
 8. Aprobe according to claim 5, further comprising: an O-ring surroundingsaid second piston sealing the space between said second piston and saidsecond piston cylinder.
 9. A probe according to claim 1, wherein: saidpressure sensor is mounted proximate said first piston with said fluidcommunication being provided by a bore extending through the wall ofsaid first piston cylinder.
 10. A probe according to claim 9, wherein:said pressure sensor is a quartz/strain gauge.
 11. A probe according toclaim 9, further comprising: d) a second piston coupled to said firstpiston; e) a second piston cylinder within which said second piston ismovably mounted, wherein movement of said second piston within saidsecond piston cylinder causes movement of said first piston within saidfirst piston cylinder.
 12. A probe according to claim 11, wherein saidsecond piston defines first and second fluid chambers in said secondpiston cylinder, each of said fluid chambers being provided with a fluidvalve such that fluid entering said first fluid chamber and exiting saidsecond fluid chamber causes said second piston to move in a firstdirection, and fluid entering said second fluid chamber and exiting saidfirst fluid chamber causes said second piston to move in a seconddirection.
 13. A probe according to claim 11, wherein: said secondpiston cylinder is mounted proximate said first piston cylinder and saidpressure sensor is mounted proximate said second piston cylinder withsaid fluid communication being provided by a bore extending through thewalls of said first piston cylinder and said second piston cylinder. 14.A probe according to claim 9, further comprising: an O-ring surroundingsaid first piston sealing the space between said first piston and saidfirst piston cylinder.
 15. A probe according to claim 11, furthercomprising: an O-ring surrounding said second piston sealing the spacebetween said second piston and said second piston cylinder.
 16. A probeaccording to claim 1, further comprising: spring biased metal protectorsurrounding said first piston cylinder.
 17. A probe according to claim16, wherein: said spring biased metal protector surrounding said firstpiston cylinder defines an annulus between said first piston cylinderand said spring biased metal protector.
 18. A probe according to claim17, further comprising: d) an elastic facing disposed in said annulus.19. A probe according to claim 18, wherein: said elastic facing isrubber.
 20. A probe according to claim 1, wherein: said pressure sensoris a quartz/sapphire strain gauge.
 21. A probe according to claim 20,further comprising: d) a second piston coupled to said first piston; e)a second piston cylinder within which said second piston is movablymounted, wherein movement of said second piston within said secondpiston cylinder causes movement of said first piston within said firstpiston cylinder.
 22. A probe according to claim 21, wherein said secondpiston defines first and second fluid chambers in said second pistoncylinder, each of said fluid chambers being provided with a fluid valvesuch that fluid entering said first fluid chamber and exiting saidsecond fluid chamber causes said second piston to move in a firstdirection, and fluid entering said second fluid chamber and exiting saidfirst fluid chamber causes said second piston to move in a seconddirection.
 23. A probe according to claim 21, wherein: said secondpiston cylinder is mounted proximate said first piston cylinder and saidpressure sensor is mounted proximate said second piston cylinder withsaid fluid communication being provided by a bore extending through thewalls of said first piston cylinder and said second piston cylinder. 24.A probe according to claim 16, further comprising: an O-ring surroundingsaid first piston sealing the space between said first piston and saidfirst piston cylinder.
 25. A probe according to claim 21, furthercomprising: an O-ring surrounding said second piston sealing the spacebetween said second piston and said second piston cylinder.
 26. Aborehole tool, comprising: a) a tool body; b) a pressure probe coupledto said tool body; and c) setting means for allowing said tool to travelthrough a borehole in a semi-set mode.
 27. A borehole tool according toclaim 26, wherein: said setting means includes a bow spring coupled tosaid tool body.
 28. A borehole tool according to claim 27, wherein: saidsetting means includes a first setting piston coupled to said bowspring.
 29. A borehole tool according to claim 28, wherein said settingmeans includes an articulated assembly coupled to said tool body and tosaid pressure probe.
 30. A borehole tool according to claim 29, wherein:said setting means includes a second setting piston coupled to saidarticulated assembly.
 31. A borehole tool according claim 26, wherein:said pressure probe includes i) a first piston cylinder having an endwhich is movable into contact with the borehole formation; ii) a firstpiston movable within said first piston cylinder; and iii) a pressuresensor in fluid communication with said first piston cylinder, whereinsaid pressure sensor is mounted at one of an interior of said firstpiston with said fluid communication being provided by a bore in thefirst piston, and proximate said first piston with said fluidcommunication being provided by a bore extending through the wall ofsaid first piston cylinder.
 32. A borehole tool according to claim 31,wherein: said pressure probe further includes iv) a spring biased metalprotector surrounding said first piston cylinder.
 33. A borehole toolaccording to claim 32, wherein: said spring biased metal protectorsurrounding said first piston cylinder defines an annulus between saidfirst piston cylinder and said spring biased metal protector.
 34. Aborehole tool according to claim 33, wherein: said pressure probefurther includes v) an elastic facing disposed in said annulus.
 35. Aborehole tool according to claim 34, wherein: said elastic facing isrubber.
 36. A borehole tool according to claim 31, wherein: saidpressure sensor is a quartz/strain gauge.
 37. A borehole tool accordingto claim 31, wherein: said pressure probe further includes iv) a secondpiston coupled to said first piston; and v) a second piston cylinderwithin which said second piston is movably mounted, wherein movement ofsaid second piston within said second piston cylinder causes movement ofsaid first piston within said first piston cylinder.
 38. A borehole toolaccording to claim 37, wherein said second piston defines first andsecond fluid chambers in said second piston cylinder, each of said fluidchambers being provided with a fluid valve such that fluid entering saidfirst fluid chamber and exiting said second fluid chamber causes saidsecond piston to move in a first direction, and fluid entering saidsecond fluid chamber and exiting said first fluid chamber causes saidsecond piston to move in a second direction.
 39. A borehole toolaccording to claim 37, wherein: said second piston cylinder is mountedproximate said first piston cylinder and said pressure sensor is mountedproximate said second piston cylinder with said fluid communicationbeing provided by a bore extending through the walls of said firstpiston cylinder and said second piston cylinder.
 40. A borehole toolaccording to claim 31, wherein: said pressure probe further includes iv)an O-ring surrounding said first piston sealing the space between saidfirst piston and said first piston cylinder.
 41. A borehole toolaccording to claim 37, wherein: said pressure probe further includes vi)an O-ring surrounding said second piston sealing the space between saidsecond piston and said second piston cylinder.
 42. A probe for use witha borehole tool for measuring pressure in an earth formation, said probecomprising: a) a first piston cylinder having an end which is movableinto contact with the formation; b) a first piston movable within saidfirst piston cylinder; c) a pressure sensor in fluid communication withsaid first piston cylinder; and d) a fluid seal between said firstpiston cylinder and said first piston.